1. Field of the Invention
The present invention relates to a pipe layout system for gasoline handling equipment, and more particularly, to a pipe layout system for service stations with secondary containment pipes and a system to test for leaks in such pipes, and most particularly, where several dispensers have the same pipeline in common.
2. Background of the Invention
For some time now, gasoline handling equipment, such as gasoline dispensers, and the piping connecting such dispensers with underground gasoline tanks and pumps has been made with secondary containment. That is, due to environmental concerns favoring prevention of leaking gasoline from entering the ground, the pipes have a second pipe around them, and the dispensers and underground pump have a box-like structure below them. An example of such a box and secondary containment is shown in U.S. Pat. Nos. 5,285,829 and 5,341,857, both to the present inventor. Typically, for each product line, such as 87 octane, there is a separate pipeline. At the dispenser, there is an impact valve which will shut off the flow of gasoline to the dispenser in the event of a vehicle colliding with the gasoline dispenser or other disaster. The above-mentioned patents show that the impact valve may also be connected to a float mechanism for detecting leaking gasoline that is collected within the dispenser. The lifting of the float mechanism will shut off the impact valve. In addition, in such systems, it is common to provide a light, bell, or other warning signal, including the shutting off of the dispenser itself, to alert the station attendant that there is a problem with that dispenser. The float system will also detect water and will operate in the same manner as in response to gasoline.
In such systems, it is industry practice and often mandatory under the fire codes or pursuant to the fire marshal's request to have a mechanism to detect leaking gasoline in the primary pipeline, which then would get into the secondary pipeline or containment boxes. At each containment box, the secondary pipeline can either be left open, as the box itself provides secondary containment, or completely closed. However, if the line is left open, it cannot be pressure-tested. Typically, codes require that the secondary line be pressurized and hold a minimum pressure, e.g., 5 psi, for a minimum time. Therefore, the secondary containment line is either closed by means of a plug inside the containment box, or closed is and connected all the way through the box. The latter structure is somewhat cumbersome.
Because of the leak detection requirement, the pipelines are inclined downward from the outermost dispenser with respect to the underground storage tank. A typical incline is one-eighth (1/8) inch per one foot of pipeline. A common distance between concrete islands center to center for each dispenser is about twenty (20) feet. The total vertical incline will be two and one-half (21/2) inches over twenty (20) feet for a 1/8 inch per foot drop. Since the pipes incline from the underground tank to the last dispenser along a pipeline, when there are several dispensers served by one product line, there can be a very significant vertical drop in the line. This necessitates the use of a different size containment box under each dispenser. Therefore, if there are three (3) dispensers, there must be three (3) different depth boxes (or one depth with three different places for penetration of the pipeline depending under which dispenser it is installed). Typically, the highest box's penetration hole is eighteen (18) inches from the concrete of the island to the middle of the primary pipeline, as a minimum required by local regulators or agencies. The next deepest holes would then be two and one-half (21/2) inches deeper, and the third deepest holes would be five (5) inches deeper. Therefore, the excavation for the deeper boxes is more cumbersome. This problem is exacerbated when service stations have more than three (3) dispensers. In fact, it is not uncommon at truck stops and the like to have about six (6) or seven (7) concrete islands. Therefore, the deepest boxes must be installed quite deep, as well as being custom-made, depending on the distance from center to center of each successive island. More importantly, a standard tank depth is about four (4) feet, but with six (6) dispensers the tank depth would have to be well deeper than four (4) feet. This would necessitate a major expense to lower the fuel tank. In a new is installation, it is still expensive to excavate deeper for the tank, and certain local requirements may prohibit too deep a tank.
It should be noted that the float leak detection system of the above-mentioned patents could be used to detect a leak in the dispenser or pump pipeline, but the impact valve only shuts down the dispenser where the box is located. If the entire product line is shut down by turning off the pump in response to detection by a float mechanism in any given containment box, this will result in significant loss of customers and lost service. In fact, providing any kind of detection in a containment box which shuts down the pump for the entire line suffers from this problem.
There is also a problem that service station attendants or owners will often disconnect the float mechanism, particularly if the box has been poorly installed and water tends to get into the box setting off the float.
In view of the above, there is a great need for a detection system which can shut down the primary (product) line, but only in response to leaks in the primary pipeline and not in response to water or a local leak within a containment box. In addition, there is a great need for avoiding excavating deeply and providing numerous types of boxes where, in particular, more than three dispensers are connected along one product line. This creates an almost impossible situation to get access inside the box from a finished concrete floor or repair a penetration fitting or a leaking pipe, or components.